Returning to its perch above 17,000 for the first time since July 29, the Dow Jones Industrial Average gained 0.4 percent. The S&P 500 finished at 1,992.37, up 0.3 percent, for its 28th record finish this year. After wavering on either side of neutral, the tech-heavy Nasdaq added 0.1 percent.

A weak yen lost its luster on Friday as Japan's benchmark Nikkei index broke a 9-day winning streak to dip below the flatline. Trade was subdued as investors stayed on the sidelines ahead of Yellen's speech.

"The Nikkei's rally has stalled, along with the dollar-yen as it consolidates near the 104 mark. It's clear the pair and the index are both waiting for a catalyst and we are unlikely to see any big moves until Janet Yellen's speech," IG's market strategist Stan Shamu wrote in a note.

Among gainers, pharmaceutical firm Shionogi held steady at a 2 percent gain while Shinsei Bank advanced 1 percent after the Nikkei business daily said the lender is planning to bid for Citigroup's Japanese retail bank operations.

Exporter stocks were mixed as the currency traded at 103.7 against the U.S. dollar. Nissan Motor added 0.3 percent while Sony pared gains to close up 0.1 percent.

Mineral sands miner Iluka Resources scaled 3.4 percent despite reporting a nearly 70 percent fall in full-year net profit on Friday. Atlas Iron was one of the worst performers on the bourse, tanking over 8 percent after announcing a one-off charge of 25 million Australian dollars on plans to divest its Shaw River Manganese interest.

Hyundai Motor remained on the watchlist as its union workers prepare to stage a partial strike later today. Shares of the carmaker overlooked the widely-expected news to trade 0.2 percent higher.

Mobile operators are also in the spotlight after being found guilty of flouting rules governing handset subsidies yet again. Apart from a 58 billion won fine, SK Telecom has been slapped with a one-week sales bans. Shares of the telco reversed early losses to rise 0.4 percent.

LG Electronics plummeted 2.7 percent despite news that it may be launching a new high end smartphone as early as October.

Political developments put Indonesian and Thai shares on the radar of investors.

Indonesia's highest court on Thursday unanimously upheld last month's presidential election result, paving the way for Joko Widodo to take over as leader of the world's third largest democracy. After opening at a 15-month high, the Jakarta Composite index closed 0.1 percent lower on Friday.